WO1994005399A1

WO1994005399A1 - Method of decomposing gaseous halocarbons

Info

Publication number: WO1994005399A1
Application number: PCT/US1993/008392
Authority: WO
Inventors: Yuichi Iikubo; John C. Qian
Original assignee: Great Lakes Chemical Corporation
Priority date: 1992-09-09
Filing date: 1993-09-07
Publication date: 1994-03-17
Also published as: EP0659102A1; CA2143956A1; EP0659102A4; JPH08501248A

Abstract

A method of completely decomposing gasesous halocarbons at temperatures of between about 500 °C and about 700 °C, preferably about 600 °C. The gaseous halocarbons may initially pass through a vaporizer tube (14), before entering the reaction tube (13). The reaction and vaporizer tubes are heated by ceramic fiber heaters (15 and 16). Temperatures were monitored and controlled by a thermocouple inserted into the heaters. Gas flows are monitored with two flowmeters. This sytem for decomposing gaseous halocarbons has the advantage of mixing the halocarbon gas with oxygen and maintaining the temperature at 600 °C for a length of time sufficient to eliminate all halocarbons from the gas.

Description

METHOD OF DECOMPOSING GASEOUS HALOCARBONS

BACKGROUND OF THE INVENTION

Field of the Invention:

The present invention relates generally to methods of decomposing gaseous halocarbons, and more particularly to a method of completely decomposing halocarbons in a gas stream at temperatures of about 600°C.

Description of the Prior Art:

A variety of halocarbon gases are produced during common commercial processes. In the prior art, it is known to combust these waste gases at temperatures on the order of 1200°C and higher in order to thermally decompose the gases to more environmentally benign products. Unfortunately, the high temperature required for these prior art processes reduces the commercial applicability of prior art methods and precludes their employment in many commercial applications.

Recently, a variety of factors have increased the

desirability of removing all halocarbons from an exhaust gas stream. In some circumstances the cost of producing

halocarbon emissions has increased, while in other

circumstances such emissions are prohibited altogether. A need has therefore remained for a method of decomposing gaseous halocarbons in an exhaust gas stream so that no halocarbons remain in the stream. The present invention addresses this need.

SUMMARY OF THE INVENTION

Briefly describing the present invention, there is provided a method of completely decomposing gaseous

halocarbons at temperatures of about 600 °C . In one aspect of the present invention , a ha locarbon gas is mixed with oxygen and heated to 600°C to eliminate all halocarbon from the gas. In a preferred embodiment, CF₄ and oxygen are mixed at a 1:2 molar ratio and are heated to 600°C to eliminate all fluorocarbon from the gas. In another embodiment, CCl₄ is completely removed from a gas by mixing the gas with oxygen at a 1:7 molar ratio and heating the mixture to 600°C.

One object of the present invention is to provide a method of decomposing gaseous halocarbons at temperatures of about 600°C to completely eliminate all halocarbon from the gas.

Further objects and advantages of the present invention will be apparent from the following description.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 is a schematic diagram of one apparatus used to test the method of the present invention according to one preferred embodiment. FIG. 2 is a schematic diagram of a second apparatus used to test the method of the present invention according to one preferred embodiment.

DESCRIPTION OF THE PREFERRED EMBODIMENT

For the purposes of promoting an understanding of the principles of the invention, reference will now be made to the preferred embodiment and specific language will be used to describe the same. It will nevertheless be understood that no limitation of the scope of the invention is thereby intended, such alterations and further modifications in the method, and such further applications of the principles of the invention being contemplated as would normally occur to one skilled in the art to which the invention relates.

The present invention relates to a method of completely decomposing gaseous halocarbons at temperatures of about 600°C. In one aspect of the invention, a gaseous halocarbon is contacted with an amount of oxygen effective to eliminate all halocarbons when the mixture is heated to a temperature of between about 500°C and about 700°C.

The gaseous halocarbons of the present invention are lower halocarbons having between one and about six carbon atoms in the chain. The halocarbon is substituted with one or more halogens, i.e., with chlorine, bromine, fluorine or iodine, either alone or in combination. Further, any one or more of the carbon atoms may be halogenated. Examples of typical halocarbons which may be decomposed by the method of the present invention include CF₄, CHF₃, CCl₄, CHCl₃,

CF₃Br and the like.

The halocarbons of the present invention may or may not include hydrogen atoms. In this description of the invention the term "halocarbon" is intended to include compounds having one or more halogens attached to one or more carbon atoms, as described above, regardless of whether hydrogen is present in the compound. These compounds therefore comprise halogens, carbon and possibly also hydrogen.

The oxygen used to contact the gaseous halocarbon may be either pure O₂ or oxygen present in a gas such as air. In all embodiments the amount of oxygen provided is at least the stoichiometric amount. In preferred embodiments, the molar ratio of oxygen to halocarbon present for the decomposition is between about 1.5:1 and about 10:1. The precise molar ratio depends on the halogenated compounds being decomposed, the reaction temperature, the contact time, the flow rate and other reaction parameters as can be appreciated by one skilled in the art. Precise ratios of oxygen to halocarbon gas may be determined for any commercial application without undue experimentation.

In the process of the present invention, the oxygen and halocarbon are heated for a time of between about five seconds and about 60 seconds or more. It is to be

appreciated that the precise contact time will depend on the halocarbons being decomposed, the temperature used in the reaction, etc. Parameters such as contact time can be optimized for a particular commercial process by those skilled in the art without undue experimentation.

The halocarbon gas used in the present invention may include only a single halocarbon or a mixture of

halocarbons. Contact times, reaction temperatures and ratios of halocarbon to oxygen may be adjusted for a particular application by one skilled in the art without undue

experimentation.

Reference will now be made to specific examples using the process described above. It is to be understood that these examples are provided to more completely describe and explain the preferred embodiments, and that no limitation to the scope or breadth of the invention is thereby intended.

Experimental Procedure One experimental apparatus is shown in FIG. 1.

Halocarbon waste gas 11 and O₂ 12 are provided to reaction tube 13, a 48" × 1/2" I.D. Inconel 600 tube. Waste gas 11 may initially pass through vaporizer tube 14 before entering the reaction tube 13. In experiments to date, the vaporizer tube 14 was a 12" × 1/2" I.D. Inconel 600 tube. The reaction and vaporizer tubes were heated by ceramic fiber heaters 15 and 16, respectively. Temperatures were monitored and controlled by a thermocouple inserted into the heaters. Gas flows were monitored with two flowmeters, both calibrated by a soap-film calibrator.

After reaction, the gases are washed in a solution 17 of dilute base, such as dilute KOH, and then a solution 18 of Na₂S₂O₃. The product gases are recovered, dried in

dryer 19 and analyzed by gas chromatography.

Another experimental apparatus is shown in FIG. 2.

Chlorocarbons 21 ( such as CCl₄ and CHCl₃) and O₂ 22 are provided to reaction tube 23. In experiments to date, the reaction tube 23 was a 48" × 1/2" I.D. Inconel 600 tube.

Both gases may initially pass through vaporizer 24 before entering the reaction tube. In experiments to date, the vaporizer tube 24 was a 12" × 1/2" I.D Inconel 600 tube. The reaction and vaporizer tubes were heated by ceramic fiber heaters 25 and 26, respectively. Temperatures were monitored and controlled by a thermocouple inserted into the heaters. Gas flows were monitored with two flowmeters, both calibrated by a soap-film calibrator.

After reaction, the gases are washed in a solution 27 of dilute base, such as dilute KOH, and then a solution 28 of Na₂S₂O₃. The product gases are recovered, dried in

dryer 29 and analyzed by gas chromatography.

In all experiments, two gas chromatography analyzers are used. One G.C. is used to separate the input gas from O₂, CO₂ and decomposed by-product. The other G.C. is used to show the content of O₂, CO₂ and decomposed by-product.

The G.C. were operated under the following conditions. G.C. #1:

Column: 3% SP-1500 on carbopack B, O.D. 5 mm × L. 3.1m, glass Detector temperature: 150°C

Detector type: TCD @ 100mA

Injector temperature: 100°C

He: 25 mL/min

Program: 30°C/4 min / 15°C/min / 110°C/3 min

G.C. #2:

Column: Carbosieve G, O.D. 5mm × L. 3.1m, glass.

Detector temperature: 180°C

Detector type: TCD @ 100mA

Injector temperature: 180°C

He: 40 mL/min

Program: 30°C/3 min / 10°C/min / 120°C/8 min The reaction contact time (θ) is calculated as follows θ = Reactor volume (155 mL) / Total flow of O₂ and

halocarbon gas

EXAMPLE 1

Decomposition of CF₃Br. This example was performed with the apparatus shown in FIG. 1. Experiments were carried out by combining O₂ and CF₃Br (Halon 1301) at the desired flow rates and temperature for one hour. The outlet gas was then sampled and analyzed by gas chromatography. Results are summarized in Table 1.

It can be seen that CF₃Br may be completely decomposed at 600°C so that no halocarbon remains. The reaction is effectively performed with a contact time of 30 seconds when the molar ratio of O₂:CF₃Br is 2:1.

The effect of molar ratio can be seen by comparing entries six through nine. In this Example, a molar ratio of 1.5:1 was not effective to completely decompose CF₃Br, while a molar ratio of 2:1 provided complete decomposition. TABLE 1

DECOMPOSITION OF CF₃Br

Flow(mL/min) Ratio Outlet Gas Content(%)

Entry Temp.(°C) Time(sec ) 1301* O₂ O₂:1301 O₂+CO₂ 1301 F-14

1 645 ~ 657 50 62 124 2:1 100 0 0

2 " 30 103 207 " 100 0 0

3 " 20 155 310 " 98.97 0 1.03

4 II 15 207 413 " 96.68 0.33 2.99

5 596 ~ 609 30 103 207 " 100 0 0

6 " 20 155 310 " 98.96 0.48 0.56

7 " 30 124 186 1.5:1 98.57 0.06 1.37

8 " " 155 155 1:1 94.56 0.18 5.26

9 " " 185 125 1:1.5 84.54 0.94 14.51

10 664 ~ 656 " 185 125 " 88.50 0 11.50

11 543 ~ 556 " 124 186 1.5:1 96.78 1.99 1.23

* Halon 1301 ( CF₃Br )

The effect of contact time can be seen by comparing entries one through four. In this Example, a reaction contact time of 20 seconds was not effective to completely decompose CF₃Br, while a reaction contact time of 30 seconds provided complete decomposition.

The effect of temperature can be seen by comparing entry 3 with entry 6, entry 7 with entry 11 and entry 9 with entry 10. As would be expected, the higher the temperature the better the decomposition. EXAMPLE 2

Decomposition of CF₃Cl. This experiment was

performed with the apparatus shown in FIG. 1. CF₃Cl and O₂ were combined at the desired flow rates and temperatures for one hour. The outlet gas was then sampled and analyzed by gas chromatography. The results are summarized in Table 2.

It can be seen that CF₃Cl is completely decomposed by mixing with O₂ at a 2:1 molar ratio (O₂:CF₃Cl) and

heating at 600°C for 30 seconds. At a molar ratio of 1.5:1 the decomposition was not complete. When the reaction

(contact) time was only 20 seconds the decomposition was not complete.

EXAMPLE 3

Decomposition of CHF₃. This experiment was performed with the apparatus shown in FIG. 1. CHF₃ and O₂ were combined at the desired flow rates and temperatures for one hour. The outlet gas was then sampled and analyzed by gas chromatography. The results are summarized in Table 3.

It can be seen that CHF₃, is completely decomposed by mixing with O₂ at a 2:1 molar ratio (O₂:CHF₃) and

heating at 600°C for 30 seconds. At a molar ratio of 1.5:1 the decomposition was not complete and CHF₃ remained in the TABLE 2

DECOMPOSITION OF CF₃CI

Flow(mL/min) Ratio Outlet Gas Content(%)

Temp.(°C) Time(sec.) F-13* O₂ O₂:F-13 O₂+CO₂ F-13 F-14**

596 ~ 608 30 103 207 2:1 100 0 0

" 20 155 310 2:1 99.69 3.31 0

" 30 124 186 1.5:1 99.96 0.04 0 " 30 155 155 1:1 98.18 1.82 0

* F-13 (CF₃CI)

** F-14 (CF₄)

TABLE 3

DECOMPOSITION OF CF₃H

Flow(mL/min) Ratio Outlet Gas Content(%)

Temp.(°C) Time(sec.) F-23* O₂ O₂:F-23 O₂+CO₂ F-23 F-14

596 - 608 30 103 207 2:1 100 0 0 " 30 124 186 1.5:1 99.95 0.047 0 " 30 155 155 1:1 88.89 11.09 0 " 30 207 103 1:2 76.31 23.40 0.29

* F-23 (CF3H)

exhaust gas. At a molar ratio of 1:2 the decomposition was not complete and both CHF₃ and CF₄ remained in the

exhaust gas.

EXAMPLE 4 Decomposition of CF₄. This experiment was performed with the apparatus shown in FIG. 1. CF₄ and O₂ were

combined at the desired flow rates and temperatures for one hour. The outlet gas was then sampled and analyzed by gas chromatography. The results are summarized in Table 4.

It can be seen that CF. is completely decomposed by mixing with O₂ at a 2:1 molar ratio (O₂:CF₄) and

heating at 600°C for 30 seconds. Further, at a molar ratio of 1.5:1 the decomposition still goes to completion and no halocarbon remained in the exhaust gas. At a molar ratio of 1:1 the decomposition was not complete and CF₄ remained in the exhaust gas.

EXAMPLE 5

Decomposition of CF₃BrCl. This experiment was

performed with the apparatus shown in FIG. 1. CF₃BrCl and 0-*, were combined at the desired flow rates and temperatures for one hour. The outlet gas was then sampled and analyzed by gas chromatography. The results are summarized in Table 5

It can be seen that CF₂BrCl is completely decomposed by mixing with O₂ at a 2:1 molar ratio (O₂:CF₂BrCl) and

heating at 600°C for 30 seconds. Further, at a molar ratio of 1.5:1 the decomposition still goes to completion and no halocarbon remained in the exhaust gas. At a molar ratio of 1.2:1 the decomposition was not complete and CF₃BrCl

remained in the exhaust gas. TABLE 4

DECOMPOSITION OF CF₄

Flow(mL/min) Ratio Outlet Gas Content(%) Temp.(°C) Time(sec) F-14* O₂ O₂:F-14 O₂+CO₂ F-14

596 - 608 30 103 207 2:1 100 0

" 30 124 186 1.5:1 100 0

" 30 155 155 1:1 89.51 10.49

F-14 (CF₄)

TABLE 5

DECOMPOSITION OF CF₂BrCl

Flow(mL/min) Ratio Outlet Gas Content(%)

Temp. (°C) Time(sec.) 1211* O₂ O₂:1211 O₂+CO₂ 1211 by-product

596 - 608 30 103 207 2:1 100 0 0

" 30 124 186 1.5:1 10 0 0 " 30 155 155 1.2:1 94.29 0 5.71

* Halon 1211 (CF₂BrCl)

F-13:4.21%, 1301 : 0.024%, F-14: 1.48%

EXAMPLE 6

Decomposition of CHF₃Br. This experiment was

performed with the apparatus shown in FIG. 1. CHF₃Br and O₂ were combined at the desired flow rates and temperatures for one hour. The outlet gas was then sampled and analyzed by gas chromatography. The results are summarized in Table 6

Again, the CHF₃Br is completely decomposed by mixing with O₂ at a 2:1 molar ratio (O₂:CHF₃Br) and heating at

600°C for 30 seconds. Also, as was the case with CF₄ and CF₂BrCl, the decomposition still goes to completion at a molar ratio of 1.5:1. At a molar ratio of 1:1 the

decomposition was not complete and CHF₃Br remained in the exhaust gas.

EXAMPLE 7 Decomposition of Trifluoropropane. This experiment was performed with the apparatus shown in FIG. 1, except that since trifluoropropane (TFP) is a flammable gas, the tests were performed with air instead of 100% O₂. TFP and O₂ in air were combined at the desired flow rates and

temperatures for one hour. The outlet gas was then sampled and analyzed by gas chromatography. The results are

summarized in Table 7.

The TFP is completely decomposed by mixing with O₂ in air at a 4:1 molar ratio (air : trifluoropropane) and heating at 600°C for 10 seconds. The higher molar ratio is required due to the dilution effect of air as an O₂ carrier.

EXAMPLE 8

Decomposition of CCl₄. This experiment was performed with the apparatus shown in FIG. 2. CCl₄ and O₂ were

combined at the desired flow rates and temperatures for one hour. The outlet gas was then sampled and analyzed by gas chromatography. The results are summarized in Table 8. TABLE 6

DECOMPOSITION OF CHFBr₂

Flow(mL/min) Ratio Outlet Gas Content(%)

Temp.(°C) Time(sec) FM-100 O₂ O₂:FM-100 O₂+CO₂ FM-100 by-product

596 ~ 608 30 110033 220077 2:1 100 0 0

" 30 112244 118866 1.5:1 100 0 0 " 30 115555 115555 1:1 99.31 0 0.69

F-13:0.057%, 1301 : 0.037%, F-14:0.597%

TABLE 7

DECOMPOSITION OF TFP

Flow(mL/min) Ratio Outlet Gas Content (%)

Temp.(°C) Time(sec.) TFP Air Air:TFP O₂+CO₂ TFP by-product

596 ~ 608 10 85 845 10:1 100 0 0

" 10 155 775 5:1 100 0 0 " 10 186 744 4:1 100 0 0 " 10 233 698 3:1 Explosion danger

TABLE 8

DECOMPOSITION OF CCI4

(600ºCº

Feed Rate Ratio Outlet Gas Content CCl4

Entry Time O₂ CCl₄ O₂:CCl4 O₂+CO₂ CCl4 Others in water

(sec.) (mL/mm) (g/min) (7o) (ppm)

1 60 138 0.111 8.5:1 100 0 0 0

2 60 138 0.122 7.8:1 100 0 0 -

3 60 133 0.130 7.0:1 100 0 0 0

4 60 133 0.165 5.5:1 98.52 1.448 0.036 -

5 45 180 0.199 6.2:1 96.90 3.077 0.027 -

6 90 81 0.124 4.5:1 99.66 0.309 0.028 -

CCl₄ was not completely decomposed by mixing with O₂ at a 2:1 molar ratio (O₂:CCl.) and heating at 600°C for

30 seconds. In fact, a molar ratio of about 7:1 was required to obtain complete decomposition. Further, contact times of about 60 seconds were used.

EXAMPLE 9

Decomposition of CHCl₃. This experiment was

performed with the apparatus shown in FIG. 2. CHCl₃ and O₂ were combined at the desired flow rates and a

temperature of about 600°C for one hour. The outlet gas was then sampled and analyzed by gas chromatography. The results are summarized in Table 9.

CHCl₃ was not completely decomposed by mixing with O₂ at a 2:1 molar ratio (0₂:CHCl₃) and heating at 600°C for 30 seconds. Here, a molar ratio of about 4.5:1, with a contact time of about 60 seconds, was required to obtain complete decomposition.

EXAMPLE 10

Decomposition of CCl. with air. This experiment was performed with the apparatus shown in FIG. 2. _CCl4 and

O₂ in air were combined at the desired flow rates and

summarized in Table 10.

CCl₄ was not completely decomposed by mixing with O₂ in air at a 12:1 molar ratio (air:CCl₄) and heating at

600°C for 30 seconds. However, at a molar ratio of about 12.5:1 and a contact time of 45 seconds complete

decomposition was obtained. TABLE 9

DECOMPOSITION OF CHCI3

Feed Rate Ratio Outlet Gas Content CHCl3/CCl4

Time O₂ CHCl3 O₂:CHCl3 O₂+CO₂ CCl3 CCl4 Others in water

(sec.) (mL/min) (g/min) (%) (ppm)

60 133 0.158 4.5:1 100 0 0 0 0/0.145

30 206 0.532 2:1 99.68 0 0.315 0 -

TABLE 10

DECOMPOSITION OF CCl₄ WITH AIR

Feed Rate Ratio Outlet Gas Content CCl4

Entry Time Air CCl4 Air:CCl4 Air+CO₂ CCl4 Others in water

(sec.) (mL/min) (g/min) (%) (ppm)

1 45 192 0.105 12.5:1 100 0 0 0

2 30 286 0.163 12:1 99.09 0.890 0.019 -

EXAMPLE 11

Repetition of the foregoing examples with other lower halocarbons, e.g. halocarbons having one to six carbon atoms, and having combinations of halogens, e.g. chlorine, bromine, fluorine, iodine, and combinations thereof, yields similar results. Advantageously, the various halocarbons are

eliminated from a gas when combined with a sufficient amount of oxygen and upon being maintained at a suitably high temperature between 500°C and 700° for a determinable period of time adequate to provide for full thermal decomposition of the halocarbons. The prior art has failed to recognize that such total decomposition of gaseous halocarbons can be accomplished at such relatively low temperatures by the use of adequate amounts of oxygen and suitable periods of

reaction time.

It is to be appreciated that the method of the present invention allows the recovery of O₂ used in the

decomposition process. Depending on the halocarbon being decomposed, rates of O₂ recovery may be as high as 100%.

Rates of recovery for typical decompositions according to the method of the present invention are shown in Table 11.

While the invention has been illustrated and described in detail in the foregoing description, the same is to be considered as illustrative and not restrictive in character, it being understood that only the preferred embodiment has been shown and described and that all changes and

modifications that come within the spirit of the invention are desired to be protected.

TABLE 11

Required O2/CFC moles and resulting O₂ recovery.

CF4 + 2 O2 ╌> CO2 + 2 OF2

2 H2O + 2 OF2 ╌> 4 HF + 2 O2 10O% 0 mol

C2F6 +7/2 O2 ╌>2 CO2 + 3 OF2

3 H2O + 3 OF2 ╌> 6 HF + 3 O2 86% 0.5 mol

C2F4 + 3 O2 ╌>2 CO2 + 2 OF2

H2O + 2 OF2 ╌> 4 HF + 2 O2 67% 1 mol

CF3Br + 2 O2 ╌> CO2 + 3/2 OF2 + 1/2 OBr2

2 H2O + 3/2 OF2 + 1/2 OBr2

- - - > HBr + 3 HF + 2 O2 100% 0 mol

CHF3 +3/2 O2 ╌> CO2 + OF2 + HF

2 H2O + OF2 + HF

- - -> 3 HF + 1/2 O2 50% 1 mol

CH2F2 + O2 ╌> CO2 + 2 HF 0% 1 mol

CH3F +3/2 O2 ╌> CO2 + HF + H2O 0% 1.5 mol

C3H3F3 + 3 O2 ╌>3 CO2 + 3 HF 0% 3 mol

Claims

CLAIMS What is claimed is:

1. A method of eliminating gaseous halocarbons from a gas containing such compounds, comprising

(a) providing a mixture of air and of the gas containing one or more gaseous halocarbons, the mixture including oxygen in an amount effective to thermally decompose all of the halocarbons in the mixture when the mixture is maintained at a temperature of between about 500°C and about 700°C;

(b) heating the gas and oxygen to a temperature of between about 500°C and about 700°C; and

(c) maintaining the mixture of gas and oxygen at about 500°C to about 700°C for a time sufficient to provide

elimination of the halocarbons.

2. The method of claim 1 wherein the mixture of oxygen and gas containing halocarbon includes an amount of oxygen effective to eliminate all halocarbons from the gas when the gas and oxygen mixture are maintained at a temperature of about 600°C, and wherein each of said heating and said maintaining is at a temperature of about 600°C.

3. The method of claim 1 wherein the molar ratio of oxygen to halocarbon is between about 1.5:1 and about 10:1.

4. The method of claim 1 wherein said maintaining is for a time of between about 5 seconds and about 90 seconds.

5. The method of claim 1 wherein said gas consists essentially of fluorocarbons.

6. The method of claim 5 wherein the molar ratio of oxygen to halocarbon is at least about 2:1.

7. The method of claim 6 wherein said maintaining is for a time of at least about 30 seconds.

8. The method of claim 1 wherein said gas consists essentially of chlorocarbons.

9. The method of claim 8 wherein the molar ratio of oxygen to halocarbon is at least about 7:1.

10. The method of claim 9 wherein said maintaining is for a time of at least about 60 seconds.

AMENDED CLAIMS

[received by the International Bureau on 27 January 1994 (27.01.94);

original claim 1 amended; other claims unchanged (1 page)]

1. A method of eliminating gaseous halocarbons from a gas containing such compounds, consisting essentially of

(a) providing a mixture of air and of the gas

containing one or more gaseous halocarbons, the mixture including oxygen in an amount effective to thermally

decompose all of the halocarbons in the mixture when the mixture is maintained at a temperature of between 500°C and 700°C;

(b) heating the gas and oxygen to a temperature of between 500°C and 700°C; and

(c) maintaining the mixture of gas and oxygen at 500°C to 700°C for a time sufficient to provide elimination of the halocarbons.

2. The method of claim 1 wherein the mixture of oxygen and gas containing halocarbon includes an amount of oxygen effective to eliminate all halocarbons from the gas when the gas and oxygen mixture are maintained at a

temperature of about 600°C, and wherein each of said heating and said maintaining is at a temperature of about 600°C.